Ed. Code, § 17550

The governing board of any school district may, when calling for bids and letting contracts for constructing new school buildings, or repairing, altering, adding to, or reconstructing existing school buildings, or demolishing existing school buildings, require each bidder for the performance of the work to agree in his or her bid to purchase and to remove from the school grounds all old materials required by the specifications to be removed from any existing school building on the same school grounds and not required for school purposes and to state in his or her bid the amount which he or she will deduct from the price bid for the work as the purchase price of the old materials. The board shall let the contract to any responsible bidder whose net bid is the lowest, or shall reject all bids.